Apparatus of the present invention relates to subsoil plow, and more particularly to a so-called subsoil chisel plow.
In recent years, subsoil plows have been used in arid regions to penetrate and to break up the soil to a depth much greater than conventional plows or other cultivating implements so as to better enable the soil to absorb and hold moisture. In non-arid regions, it has been found that repeated plowing with conventional moldboard plows only cultivates the top 10 inches (25.4 cm) of soil leaving the soil therebelow undisturbed. Repeated plowing year after year with moldboard plows maintains the top layer of soil well broken and aerated for the crops, but a hard pan or plow sole develops in the undisturbed subsoil. This plow sole does not readily absorb moisture and oftentimes acts as a moisture barrier which causes much moisture to run off the field. Also this hard plow sole prevents crops from sending down deep root systems. In short, it is only the cultivated top layer of soil which retains the majority of moisture for the crops and supports the crop root systems.
It is known that by using subsoil chisel plows or rippers which penetrate the ground to a much greater depth (for example, 16 inches or more) than conventional moldboard plows, this plow sole can be broken up. If a field is plowed with a subsoil plow in the fall after the crops have been harvested, winter rain and snow will percolate through the soil to fully soak the ground to a depth below the level of the plow sole and the crop root systems will readily penetrate the soil to a much greater depth. This increased amount of subsoil moisture and greater root depth of the crops has resulted in crops which are better able to withstand drought conditions.
Another advantage of a subsoil plow is that the subsoil plow may be relatively wide (e.g., having a width of up to 20 feet or more) and that by using a powerful tractor, the subsoil plow may be pulled through the field at a relatively high rate of speed. In conventional subsoil plows, the plow teeth are commonly secured to the plow frame by means of a shear pin or bolt so that in the event a plow tooth strikes an underground object (e.g., a rock), the shear pin will fail thus releasing the plow tooth so as to swing up out of the ground and to thus limit the maximum force applied to the plow tooth and to the plow. However, in conventional subsoil plows, the plow tooth must dig deeper into the ground after the shear pin fails as it swings to its retracted position thus placing great strain on the plow tooth and the plow frame which can result in damage thereto.
Also, tractors capable of pulling subsoil plows are conventionally equipped with either a category 2 or a category 3 three point hitch. These tractor hitches have been standardized so that any tractor having a category 2 hitch may be readily hitched to an implement designed for a category 2 hitch or any tractor having a category 3 hitch may be readily hitched to any category 3 implement. Many of these tractor hitches utilize a so-called automatic coupler which enables an implement to be hitched to the tractor without the driver leaving his tractor seat merely by backing the tractor up to the implement aligning the tractor hitch with the implement hitch, and engaging coupling hooks on the tractor hitch with the hitch pins on the implement. Generally, a category 3 hitch is wider than a category 2 hitch and is of more sturdy construction. Also, with the category 2 hitches, a larger diameter hitch pin on the implement must be used if the category 2 hitch is equipped with an automatic coupler. Oftentimes a farmer will own two or more tractors of sufficient size to pull an implement, but the tractors may have different hitches. Thus, with most conventional implements, only the tractor having the hitch for which the implement was designed may be used to pull the implement. One known implement hitch arrangement utilizes hitch pins held by brackets of sufficient length so that either a category 2 or category 3 tractor hitch may be coupled to the hitch pins. It has been found, however, that these relatively long hitch pins will bend when subjected to high loading as may be required to pull a large subsoil plow or other similar implement through a field at high speed.
Recently, a tractor hitch designated category 3N has been offered by John Deere & Company of Moline, Ill., and by other tractor manufacturers which combines the narrow width of a category 2 hitch with the greater height and strength of a category 3 hitch. The purpose of the category 3N hitch is to allow owners of a larger tractor equipped with the category 3 hitch to use implements intended for use with a category 2 hitch. Manufacturers of this category 3N hitch state that it may be necessary to drill an extra hole in the center implement hook hitch mast on the implement. Thus, owners of tractors equipped with a category 3 hitch still must buy the category 3N hitch to use category 2 implements with the tractor.
Reference may be made to U.S. Pat. Nos. 1,531,643, 2,209,083, 2,808,772, 3,450,212 and 3,559,747 showing various chisel plows or earth rippers in the same general field as the subsoil plow of the present invention.